Both light efficiency and dynamic range are major concerns for commercial projector designs. High contrast and peak luminance are vital for higher perceived image quality (brightness, colorfulness) [Rempel et al. 2009], even if most images only require a small amount of localized very bright highlights above their average picture level in order to appear realistic [Rempel et al. 2011]. On the other hand, an optical system should be highly efficient to minimize power consumption, and simplify thermal management. The latter concern makes it impractical to achieve very high peak brightness by boosting the power of a projector light source.
Amplitude spatial light modulators (or SLMs) are often used to create tones and colors in images by pixel-selectively blocking light. Such SLMs tend to be optically inefficient since blocked light is absorbed.
HDR (high dynamic range) image projection may be achieved by providing two or more stages of light modulators (Hoskinson et al.). Many light modulators (e.g. LCD panels) generate a desired light field by subtraction (i.e. by absorbing unwanted light). Some efforts have been made to create desired light fields by reallocating light. However, many available light reallocation technologies have significant disadvantages. For example, some require laser light, which can result in laser speckle. Some are very computationally intensive. Some require very high spatial frequency control of light which places demands on light modulators and also can result in artifacts caused by diffraction of light.
Freeform lenses, which can be aspherical, asymmetric lenses may be designed to generate specific caustic images under pre-defined illumination conditions [Finckh et al. 2010, Papa et al. 2011, Schwartzburg et al. 2014, Yue et al. 2014]. The caustic image is a redistribution or “reallocation” of light incident on the freeform lens [Hoskinson et al. 2010], Computer graphics approaches to designing such freeform lenses are known as goal-based caustics. Designing a freeform lens to achieve a particular desired image can be computationally intensive.
Freeform lenses may be applied for general lighting applications (e.g. [Minano et al. 2009]) and more specifically for goal-based caustics [Berry 2006, Hullin et al. 2013]. Some methods for designing freeform lenses apply discrete optimization methods that work on a pixelated version of the problem (e.g. [Papas et al. 2011, Papas et al. 2012, Papas et al. 2012]). Others optimize for continuous surfaces without obvious pixel structures (e.g. [Finckh et al. 2010, Kiser et al. 2013, Pauly and Kiser 2012, Schwartzburg et al. 2014, Yue et al. 2014]).
Holographic image formation models (e.g. [Lesem et al. 1969]) have been adapted to create digital holograms [Haugen et al. 1983]. Holographic projection systems have been proposed for research and specialty applications [Buckley 2008]. Many of these systems use diffraction patterns (or holograms) addressed on a phase SLMs in combination with coherent light (lasers) for image generation. While in principle an efficient way to form an image, the challenges in holography for projectors lie in achieving sufficiently good image quality, the limited diffraction efficiency achievable by binary phase modulators [Buckley 2008], and the requirement for a Fourier lens, often resulting in a bright DC spot within the active image area or reduced contrast throughout the image due to an elevated black level (in cases where the DC spot is expanded). Holographic projection generally requires coherent light.
The inventors have recognized a need for more efficient ways to design freeform lenses to achieve desired light patterns. In particular, the inventors have determined that sufficiently efficient design methods may be applied to provide real-time or near real time generation of dynamic freeform lenses. Such dynamic freeform lenses may, for example deliver video content or dynamically-changing light effects.